The present invention relates to a method for forming a pattern using a photoresist film in the manufacturing process of semiconductor device, and more particularly, to a method for forming a pattern which can be manufactured by using only the two layer photoresist film by silylating the photoresist film, having maintained the resolution increasing effect which is caused by a multi-layer resist film process (hereinafter, called "MLR" process).
In general, the thickness of a first photoresist film disposed directly over the wafer differs from that of a second photoresist film disposed over the first photoresist film. Accordingly, in the subsequent exposure process the second thin photoresist film is excessively exposed while the thick first photoresist film is insufficiently exposed. Therefore, during the development process, the line width of the resist pattern varies. Specifically, the line width of the overexposed second photoresist film becomes much narrower than the underexposed first photoresist film.
In addition to this problem, the minimum resolution value is decreased due to the so-called standing wave effects in the thick-formed first resist layer, and the reflected lower substrate also makes the resolution worse.
Also, when the thin second resist film is used, the problem of the standing wave effect and the lowering of the resolution generated from the reflective substrate can be overcome. However, it is impossible to overcome the limitation of the step coverage.
To overcome the above problem, an MLR process has been proposed. This processing combines the thick planarized resist layer and the thin image transcribing layer, thereby forming the resist pattern (see Silicon Processing for the VLSI Era, S. Wolf and R. N. Tauber, Vol. 1, 1986, pp 424).
The conventional method for forming the pattern by the general known MLR processing will be explained with reference to the attached FIGS. 1A to 1H.
First, as shown in FIG. 1A, a first photoresist layer 11 is formed on a wafer 10. Though wafer 10 is shown as flat, the surface of the wafer includes the various step region depending on the shape of the surface. The first photoresist layer 11 is formed thick enough to flatten this surface.
Then, as shown in FIG. 1B, first photoresist layer 11 is neutralized, and is soft-baked on a hot plate for I minute or more at the temperature of 200.degree.-250.degree. C., in order to vaporize the solvent in the resist. At this time, the resin component in first photoresist layer 11 and the photo active compound (PAC) are cross-linked, to thereby form a hardened first photoresist pattern 12.
Then, as shown in FIG. 1C, an oxide film 13 is deposited thin on the hardened first photoresist layer 12. As another method, the oxide film of silane (SiH.sub.4) base is dispersed and spinned at the spin on glass (SOG) spin coator, and baked at a temperature of 200.degree.-240.degree. C., thereby forming the oxide film 13.
Then, as shown in FIG. 1D, a second photoresist layer 14 is deposited thin on the oxide film 13.
Then, as shown in FIG. 1E, a ultra-violet light 15 is first irradiated to a photo mask 16 wherein the predetermined pattern is formed, and transcribes the pattern formed in photo mask 16 to second photoresist layer 14.
The PAC component of the region of second photoresist layer 14 lighted through photo mask 16 is destroyed, which then is washed by the developing solution in the subsequent development process.
As shown in FIG. 1F, a second photoresist pattern 18 remains and is formed by the development process. Only the portion of second photoresist layer 14 which was not irradiated to the ultra violet light 15 remains.
Then, as shown in FIG. 1G, an oxide film pattern is formed by etching an oxide film 13 formed in the lower part using second photoresist pattern 18 as an etching mask layer.
As shown in FIG. 1H, first photoresist layer 12 is etched using the pattern of oxide film 13 as an etching mask layer. As a result, a pattern consisted of the first photoresist layer 12 and oxide film 13 are formed on wafer 10.
A method for forming the pattern by the conventional MLR processing transcribes well the pattern of the photo mask, even a wafer whose surface is extremely uneven. Therefore, the resolution is increased and the depth of focus becomes deeper.
However, in the conventional MLR processing, the resist has to be formed twice and the oxide film has to be formed as an intermediate layer, which requires a baking process performed at a high temperature. Facilities for etching the oxide film are additionally needed. The addition of this complicated processing results in lower productivity, increased density, and increased cost.
Additionally, when the conventional MLR method is used, the by-products of the structure material such as a polysilicon layer, oxide film, or a metal layer formed on the wafer become attached to the sidewall of the resist in the course of etching the resist film. These by-products react with the resist, thereby forming a polymer. This polymer remains even after the resist removing process is completed, and causes further defects.